Processes of forming semiconductor devices and of manufacturing semiconductor wafers include an ion implantation process. In the ion implantation process, a desired element is ionized and the resultant is added into a semiconductor wafer.
In typical ion implantation operation, n-type impurities such as arsenic, phosphorus, and antimony, or p-type impurities such as boron, which are impurities of a dopant type, are implanted from a surface of a semiconductor wafer with an ion implantation apparatus to form n-type or p-type semiconductor region.
In comparison with a diffusion method of adding impurities, the ion implantation method, which has been widely used as a method of adding impurities of a dopant type, has advantages that a photoresist can be used as a mask, the amount of impurities and an ion implantation depth can be accurately controlled, and the spread of impurities in a lateral direction can be inhibited.
When light elements such as hydrogen are implanted from the surface of a semiconductor wafer (a bond wafer), the wafer is bonded to a base wafer as a foundation through an insulator film, and the resultant bonded wafer is then subjected to a heat treatment and so on, the bond wafer is delaminated at a ion-implanted layer due to a function of the light elements implanted into the semiconductor wafer, and consequently a semiconductor thin film layer is transferred on the base wafer.
This method is referred to as the ion implantation delamination method (also referred as to the SMART-CUT (a registered trademark) method) and used to manufacture an SOI (Silicon On Insulator) wafer.
The basic principle of the ion implantation apparatus used in the ion implantation is that a source gas containing a desired implanted species is ionized by the arc discharge or microwave discharge and the ions are accelerated with an electric field. The track of the accelerated ions is bent with a magnetic field in a mass spectrograph to separate the implanted species and an unnecessary charged species. Only the implanted species extracted in this manner is implanted from the surface of the semiconductor wafer. The ion implantation depth of the implanted species is adjusted by accurate control of accelerating voltage and its implantation amount is adjusted by accurate control of beam current.
Since the implanted species, i.e. ions, are implanted in the form of a beam, implanting ions over the entirety of the wafer surface requires beam scanning or wafer movement.
The ion implantation apparatus is divided into a batch type apparatus (See FIG. 1), implanting ions simultaneously into a plurality of wafers, and a single wafer processing type apparatus, implanting ions into a wafer.
For example, as shown in FIG. 1, the batch type ion implantation apparatus 10 takes out ions produced from an ion source 16 by applying the electric field and accelerate the ions with a first accelerator 17a. In the apparatus, a mass spectrograph 15 then conducts a mass analysis with the magnetic field to extract only ions having a predetermined mass. A second accelerator 17b further applies the electric field to accelerate the ions for the second time (second acceleration). The ion beam 18 accelerated in this manner is irradiated to the surface of the semiconductor wafers W in a chamber 14.
Here, the semiconductor wafers W are placed on a wafer supporting member. In the wafer supporting member, the semiconductor wafers W are lined up and disposed on a wheel 11, which is a circumference portion having a certain radius. The wheel 11 is rotated about a wheel center 11a at a high speed, e.g., a rotational speed of 800 to 900 rpm and a peripheral speed of 50 m/sec, so that ions can be implanted into the wafer plane uniformly in the direction of the circumference of the wheel 11.
On the other hand, there are two methods for implanting ions in the direction of the radius of the wheel as follows: (1) the wheel is radially moved while the beam is fixed; (2) beam scanning in the direction of the radius of the wheel is performed but the wheel is not radially moved. The scanning speeds in a radial direction in both methods are low, e.g., 1 to 10 cm/sec.
Similarly with the batch type ion implantation apparatus, the single wafer processing type apparatus radially moves a wafer supporting member or performs beam scanning in a radial direction so that ions can be implanted over the entirety of the wafer surface.
When the implanted species are needed to be uniformly implanted over the entirety of the surface of the semiconductor wafer in the ion implantation operation, the implanted species may be non-uniformly implanted due to the state of the ion beam, malfunction of the apparatus, and so on.
Patent Document 1 discloses that, when ion implantation concentration varies in the wafer plane during hydrogen ion implantation, a cleavage plane may become uneven reflecting the variation.